1. Field of the Invention
The present invention relates to an improved secure self learning system and method and, in particular, to an improved secure self learning system and method for remotely controlling systems and devices in security systems.
2. Discussion of the Background
The remote control of systems or devices via ultrasonic, radio frequency or infra red transducers is popular for many applications, including security systems for buildings and vehicles, and remote controlled garage door and gate openers. Certain unidirectional transmission systems currently in use have two very important security shortcomings: (a) the codes they transmit are usually fixed; and (b) the number of possible code combinations is relatively small. Either of these shortcomings can lead to unauthorized access.
The limited number of possible combinations available in most remote control systems makes it possible to transmit all possible combinations in a relatively short time. A hand held microprocessor-based system for this purpose (called a code scanner) can easily be constructed.
In systems using eight DIP switches (256 combinations), this scanning process can typically be accomplished in less than 32 seconds, when trying eight combinations per second. Even in systems using 16 bit keys, yielding 65,536 combinations, only 2 1/4 hours would be required to try all possible combinations. It should also be noted that the scanner may gain access in far less time than this maximum time and the average time would, in fact, be half of the total time.
An easier way of gaining unauthorized access to a security system is freely available. A unit of this type is advertised as a tool for the "legal repossession of vehicles." A remote control transmitter of the type normally used in vehicle security and remote control systems includes a small radio transmitter that transmits a code number on a specific frequency. This code number is normally generated by an integrated circuit encoder. This transmission frequency is usually fixed by legislation within a particular country. Thus, it is possible to build a receiver that can receive signals from all such transmitters and to use this together with a circuit which records the transmissions captured by the receiver. Such a device is known as a code or key grabber and can be used to gain access to protected premises or to vehicles with remote control security systems.
Code hopping and rolling code systems are currently available to overcome the limitations of fixed code systems (refer to ZA Patent No. 91/4063 and U.S. Pat. No. 5,103,221). The specifications of these patents describe transmitters which use algorithms to generate a different transmission each time the transmitter is activated. When a code is received and decoded, a decoder responds only if a valid transmission was made. In some cases (refer to ZA Patent No. 91/4063) a special algorithm is used with a stored key to decode an encoded reception. The decoded value is then compared to a stored value to determine if the transmission is legitimate or not.
A disadvantage of code hopping and rolling code systems is the fact that it is difficult to replace or disable lost, stolen or unserviceable transmitters. External equipment must be used by a manufacturer or dealer to reprogram and replace a transmitter. An additional security problem may be created during this process.
Ideally, a security system should not require dealer intervention when a user needs to add a new transmitter to the system or replace a transmitter. The user should be able to buy a generic replacement transmitter off the shelf and add this transmitter unassisted when convenient. Learning systems provide this capability, in that the decoder can "learn" the new transmitter's identity without having to be reprogrammed from outside using special equipment.
A learning system should however not only enable a user to add a new transmitter to the system, but should also have a means of excluding a previous transmitter from the system, due to the possibility of such a transmitter falling into the wrong hands.
In self learning fixed code systems, the incoming code is stored for future references by the decoder when it is in a learning mode. Subsequent transmissions are compared with the learned code. Different arrangements to learn new transmitter codes are used. A switch can be used to set the decoder either in a normal operation mode or in a learning mode (U.S. Pat. Nos. 4,750,118 and 4,912,463). In the learning mode, the decoder can learn new valid codes from a transmitter. Similar means are used (refer to U.S. Pat. Nos. 4,931,789 and 5,049,867) to program the decoders to react to a new transmitter code. In another patent (refer to U.S. Pat. No. 5,148,159), a randomly selected fixed code is generated by the decoder and programmed into the associated transmitter. U.S. Pat. No. 4,855,713 describes the use of a hand held programmer to program the new fixed code to be recognized by the decoder. In all of these patents, the transmitted or programmed codes are fixed stored codes. Security threats by means of code grabbing or code generation still exist irrespective of the learning mechanisms employed. In addition, for these systems to learn, the user has to either (1) use a cumbersome, more expensive, two switch system; and/or (2) the user has to set the receiver/decoder in learning mode via (a) a switch inconveniently physically located on the receiver/decoder which can be very difficult (if not impossible for elderly or handicapped persons) to activate once the system, e.g., a receiver of a garage door opening system, is installed, e.g. on the ceiling of a user's garage (See FIG. 1 of U.S. Pat. No. 4,750,118), (b) a code sent by the transmitter--activation and use of such can be complicated and not secure if the transmitter is lost or worse stolen, or (c) a code sent by a separate programming means which can be complicated to use and likewise not secure if the programming means is lost or worse stolen.
Reference should also be made to the specifications of the following U.S. Pat. Nos.: RE 29,525; 4,380,762; 4,385,296; 4,426,637; 4,529,980; 4,534,333; 4,574,247; 4,590,470; 4,596,985; 4,638,433; 4,652,860; 4,686,529; 4,737,770; 4,779,090, 4,835,407; 4,847,614; 4,855,713; 4,878,052; 4,890,108; 4,928,098; 4,951,029; 4,988,992; 5,049,856; and 5,055,701.